My primary goal is to understand how mutational activation of K-RAS induces high grade dysplasia early during the malignant progression of colorectal cancer. My working hypothesis is that mutant K-RAS signals through the B-RAF kinase to suppress the differentiation of benign colonic tumor cells. The proposed studies include targeted investigations aimed at gaining mechanistic insight into known RAS effector pathways and exploratory studies aimed at identifying novel effectors of K-RAS signaling. I propose three specific aims: Aim 1. Analyze the phenotypic effects on the intestinal epithelium of activating K-ras, H-ras, or N-ras. Aim 2. Determine the relevance of candidate effector pathways to K-ras-induced tumor progression. Aim 3. Identify novel signaling effectors of mutationally activated K-ras. My studies will utilize both in vitro and in vivo experimental systems, namely human colorectal cancer cell lines and genetically engineered mice. Parallel studies conducted in these complementary systems will yield the greatest amount of insight into the oncogenic properties of K-RAS signaling. To successfully complete the Specific Aims, I will use small molecule inhibitors, genome-wide phosphoproteomic analysis, and emerging shRNA technology to dissect the signaling pathways that are required for oncogenic K-RAS to promote tumor progression. In the end, I am confident that therapeutic targeting of the RAS signaling pathway will represent a powerful means of fighting the malignant progression of colorectal cancer. Relevance to public health: In January, 2005 the American Cancer Society announced that cancer has replaced heart disease as the number one cause of death in the United States. Colorectal cancer alone accounts for more than 50,000 deaths per year in this country. Despite all that we have learned about the molecular pathogenesis of colorectal cancer, mortality due to this disease has remained constant over the past twenty years. Through my functional studies of the K-RAS oncogene, I aim to identify molecular targets for novel therapeutics that will eradicate colon cancer.